Industrial ultrasonic transducer heads secured to the outside of a pipe for determination of the flow of fluids have been constructed as shown in U.S. Pat. No. 4,208,908-Hickox, with the transducers completely imbedded in an epoxy resin and with the surface of the transducer head having a flat surface. Upon mounting of the transducer head to the outer wall of the pipe, there is a line contact between the head and the pipe and the space between the outer wall of the pipe and the flat surface of the transducer head is generally filled with an acoustic couplant or a suitable adhesive such as an epoxy resin.
Such transducer head configuration made it difficult to properly apply the transducer head to the outside wall of the pipe because of the tendency of the flat surface of the transducer head to rock on the round surface of the outer wall of the pipe. Additionally, it was difficult with the imbedding technique to obtain accurate angular alignment of the transducers in their mountings to provide a precise control of the angle of the transducer relative to the axis of the pipe. Furthermore imbedding the ultrasonic transducer in an epoxy resin subjects the transducer to mechanical stresses that results in decreased sensitivity. Finally, it was not possible to perform any calibration or operating checks on the transducer head before the transducers themselves were completely encapsulated within the head. After encapsulation, of course, it was not possible to make any changes to correct problems that would occur to make the transducer head inoperative.